Method and apparatus for localized gear tooth root fillet shot peening

ABSTRACT

A method of manufacturing a gear having root fillets between adjacent teeth that are shot peered to improve compressive strength. A robot moves a shot peening nozzle between adjacent teeth. A servomotor drive indexes the gear in increments corresponding to one or more teeth. The nozzle has a tapered tip that is moved between adjacent tooth faces with clearance relative to the tooth faces.

REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Ser. No. 62/468,474 filed Mar. 8, 2017, the disclosure of which is hereby incorporated in its entirety by reference herein.

TECHNICAL FIELD

This disclosure relates to manufacturing gears that are subjected to shot peening to harden localized areas of the gear teeth and, in particular the root diameter of the gear teeth.

BACKGROUND

Shot peening imparts compressive stress into gear root fillets for improved bending fatigue.

Shot peening is performed on gears with static nozzles disposed at a large stand-off distance from the gear to create a large blast area pattern. This large blast area randomly hits gear teeth tips and flanks that do not require peening.

The tips of the congruently cut root to face angles can have edge radii cut during the cutting process. However, some gears such as face milled gears have non-congruent root and face angles which require an additional operation to apply edge radii. Edge radii are added to reduce edge chipping, edge rolling (into gear mesh contact), and subsurface fracturing that may be caused by high intensity shot peening.

In some gear manufacturing processes, lapping, or electrochemical machining may be specified after shot peening to remove or reduce edge chipping edge rolling and fracturing. Other secondary operations may be specified to prevent quality defects and reduce flank peening which can also be manifested in the form of gear wear or fretting. These imperfections can result in excessive or premature gear or bearing wear and may also cause noise, vibration and harshness quality control issues.

This disclosure is directed to solving the above problems and other problems as summarized below.

SUMMARY

According to one aspect of this disclosure, a method of manufacturing a gear is disclosed in which root fillets of the gear are shot peened to add compressive strength to the surface and the sub-surface area of the root fillets. The method includes the steps of forming a gear including a body and a plurality of teeth and assembling the gear to a servomotor drive. A robot provided with a shot peening system having a nozzle directs shot media at root fillets through a nozzle opening disposed between faces of two adjacent teeth. The servomotor drive incrementally rotates the gear and the robot shot peens along a length of the root fillets.

According to other aspects of this disclosure the nozzle may be spaced from the root fillets less than the depth of the depth of the teeth. The nozzle may be oriented to direct shot aligned with a length of the root fillet at an approach angle to the target area of the part of between 20 and 70 degrees offset from the tangent line of the root fillets.

The servomotor drive rotates the gear in single tooth increments and the robot follows the length of the root fillets on opposite side of each tooth between each single tooth increment.

The gear may be a pinion gear, a ring gear or any other type of gear that requires shot peening of the root fillet between adjacent teeth for improved compressive strength.

According to another aspect of this disclosure, a nozzle is provided for shot peening a gear in the area of the root fillet between a plurality of teeth. The nozzle includes an air inlet, a shot feeder and a nozzle tip. The nozzle tip receives air under pressure from the air inlet and shot from the shot feeder. The nozzle tip directs shot at the root fillets through a nozzle opening disposed between the faces of two adjacent teeth as the nozzle tip is moved along a length of the root fillets.

According to other aspects of this disclosure as it relates to the nozzle tip, the nozzle tip may define a nozzle opening that is spaced from the root fillet to provide a blast diameter greater than the inner diameter of the nozzle opening. The nozzle tip is tapered to fit with clearance within the spacing between two adjacent teeth. The nozzle is positioned between two teeth with at least two millimeters of clearance from the faces of the teeth when held at a specified standoff distance from the root fillet.

The shot media may be cut wire shot or spherical shot having a diameter of between 0.5 and 0.8 mm, however, this disclosure may be applicable with shot media ranging from 0.3 to 1.6 mm. The nozzle tip may define a nozzle opening that is at least four times the diameter of the shot media.

The nozzle tip defines a nozzle opening may be between 35% and 75% of the width of the root fillets.

The above aspects of this disclosure and other aspects will be described below with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a robot and a fixture including a servomotor drive holding a pinion gear in position for shot peening.

FIG. 2 is a perspective view of a hypoid pinion gear having root fillet areas being shot peened with a shot peening system including a nozzle.

FIG. 3 is a diagrammatic view of a nozzle and shot peening system.

FIG. 4 is a diagrammatic view of a nozzle of the shot peening system disposed between two adjacent gear teeth directing shot media at the root fillet of the gear.

FIG. 5 is a fragmentary perspective view of a pinion gear showing the path of movement of the robot as the shot peening system is moved between adjacent gear teeth and the direction the servomotor drive indexes the pinion gear.

FIG. 6 is a fragmentary perspective view of a ring gear showing the path of movement of the robot as the shot peening system is moved between adjacent gear teeth and the direction the servomotor drive indexes the ring gear.

DETAILED DESCRIPTION

The illustrated embodiments are disclosed with reference to the drawings. However, it is to be understood that the disclosed embodiments are intended to be merely examples that may be embodied in various and alternative forms. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed are not to be interpreted as limiting, but as a representative basis for teaching one skilled in the art how to practice the disclosed concepts.

Referring to FIG. 1, a robot is generally indicated by reference numeral 10. A servomotor drive 12 is shown in a fixture that is part of a shot peening system 14. The servomotor drive 12 is shown holding a pinion gear 16 in position to be shot peened.

Referring to FIG. 2, the pinion gear 16 is shown to include a plurality of gear teeth 18. In the illustrated embodiment, the gear teeth are hypoid pinion gear teeth but it should be understood that other types of gears having different types of gear teeth may be processed according to the disclosed method and system.

A root fillet 20 is provided between adjacent gear teeth 16 that is subjected to the shot peening operation to add compressive strength to the root fillet 20 surface and the sub-surface area below the root fillets 20. The sides 24 of the pinion gear teeth extend radially outwardly from the root fillets 20. The tops 26 of the pinion gear teeth 16 are provided at the radial outermost portion of the pinion gear 16.

Referring to FIG. 3, a nozzle 32 is illustrated that is part of the shot peening system 14. The nozzle 32 includes a pressurized air inlet 36 that receives compressed air from a compressed air supply 38 such as an air compressor. A shot media feeder 40 supplies shot media to the nozzle and receives shot media from a shot media supply magazine 42. The shot media may be cut wire shot or spherical shot and may range in diameter from 0.3 to 1.6 mm.

The compressed air and shot media 46 are directed to the root fillet 20 from a position between two adjacent teeth 18. The nozzle 32 is moved by the robot 10 between the adjacent teeth 18 with the tip of the nozzle radially inboard relative to the tops 26 of the pinion gear teeth. In this way, the edges of the teeth between the tops 26 and the sides 24 do not become damaged by the shot peening operation.

The nozzle tip 44 defines an opening that is held spaced from the root fillet 20 to provide a blast diameter greater than the inner diameter of the opening and to shot peen the full width of the root fillet 20 and possibly the inner radial portion of the sides. Stated another way, the nozzle tip 46 may define a nozzle opening which may be between 35% and 75% of the width of the root fillets.

Referring to FIG. 4, the nozzle tip 44 is shown shot peening a root fillet 20 while being disposed beside the gear tooth 18 sides 24. The nozzle 32 is tapered to fit with clearance between the spacing between two adjacent gear teeth 18. The nozzle 32 is positioned between two gear teeth 18 with at least two millimeters of clearance from the faces of the teeth when held at a specified standoff distance from the root fillet 20.

The shot media 46 may be cut wire shot or spherical shot having a diameter of between 0.5 and 0.8 mm. It should be understood that this disclosure may be applicable to shot peening systems using shot media ranging from 0.3 to 1.6 mm. The nozzle tip defines a nozzle opening that is at least four times the diameter of the shot media.

Referring to FIG. 5, a pinion gear 16 is shown with an arrow I on the end of the pinion gear 18 to illustrate the direction of rotation of the pinion gear 18 when the servomotor drive rotates the pinion gear 18. The rotation is incremental and may be a rotation of a single gear tooth 18. Alternatively, the incremental rotation may be several tooth widths depending upon the cycle time and coordination with the robot 10 moving the shot peening system 14.

The robot 10 moves along a path indicated by the serpentine arrow P. If the servomotor drive 12 moves in single tooth increments, the robot 10 will trace the length of the root fillet 20 in one direction and will trace the next root fillet 20 in the opposite direction. The nozzle 32 is held at an angle of between 20 and 70 degrees from the tangent line of the root fillet 20 to avoid damage to the nozzle from shot media bouncing off the root fillet 20 and back to the nozzle tip 44.

Referring to FIG. 6, a ring gear 48 is illustrated that may be shot peened in a similar manner to the pinion gear 18 shot peening process as described above. The ring gear 48 has root fillets 50 that are radially outboard of the inner tips 52 of the gear teeth 54. The root fillets 50 are shot peened to add compressive strength to the root fillet 50 surface and the sub-surface area below the root fillets 50. The robot 10 moves along a path indicated by the serpentine arrow P. The servomotor drive 12 moves the ring gear 48 in the direction of the arrow I in single tooth increments, as the robot 10 traces the length of the root fillets 50 in one direction. The servomotor drive 12 moves the ring gear 48 and traces the next root fillet 50 in the opposite direction.

The embodiments described above are specific examples that do not describe all possible forms of the disclosure. The features of the illustrated embodiments may be combined to form further embodiments of the disclosed concepts. The words used in the specification are words of description rather than limitation. The scope of the following claims is broader than the specifically disclosed embodiments and also includes modifications of the illustrated embodiment 

What is claimed is:
 1. A method of manufacturing a gear comprising: forming a gear including a body and a plurality of teeth; assembling the gear to a servomotor drive; and providing a robot with a shot peening system having a nozzle directing shot at root fillets through a nozzle opening disposed between faces of two adjacent teeth, wherein the servomotor drive incrementally rotates the gear and the robot shot peens along a length of the root fillets.
 2. The method of claim 1 wherein the nozzle is spaced from the root fillets less than a depth of the teeth.
 3. The method of claim 1 wherein the nozzle is oriented to direct shot aligned with a length of the root fillet at an approach angle offset between 20 and 70 degrees from a tangent line of the root fillets.
 4. The method of claim 1 wherein the servomotor drive rotates the gear in single tooth increments and the robot follows the length of the root fillets on opposite sides of each tooth between rotation increments.
 5. The method of claim 1 wherein the gear is a pinion gear.
 6. The method of claim 1 wherein the gear is a ring gear.
 7. A nozzle for shot peening a gear having a plurality of teeth comprising: an air inlet; a shot feeder; and a nozzle tip receiving air under pressure from the air inlet and shot media from the shot feeder, wherein the nozzle tip directs the shot media at root fillets through a nozzle opening disposed between faces of two adjacent teeth as the nozzle tip is moved along a length of the root fillets.
 8. The nozzle of claim 7 wherein the nozzle tip defines a nozzle opening having an inner diameter and is spaced from the root fillet to provide a blast diameter greater than the inner diameter, wherein the shot media is directed towards a space between two adjacent teeth.
 9. The nozzle of claim 7 wherein the nozzle defines a nozzle opening and is tapered to a radius that fits between two adjacent teeth with at least two millimeters of clearance away from the faces of the teeth when the nozzle opening is held at a specified standoff distance from the root fillet.
 10. The nozzle of claim 7 wherein the shot media is cut wire shot having a diameter of between 0.02 and 0.032 mm.
 11. The nozzle of claim 7 wherein the nozzle tip defines a nozzle opening that is at least four times a diameter of the shot media.
 12. The nozzle of claim 7 wherein the nozzle tip defines a nozzle opening that is between 35% and 75% of a width of the root fillets. 